1. Field of the Invention
This invention relates to a signal processing circuit for separating a sync signal from a video signal. The signal processing circuit of this invention can be used in a magnetic recording apparatus. This invention also relates to a signal processing apparatus.
2. Description of the Related Art
Some video tape recorders (VTR""s) are based on a standard format referred to as a VHS format. There is an S-VHS format which improves over the VHS format. A VTR of the S-VHS standard can record and reproduce a video signal which is wider in frequency band and higher in picture quality than a video signal handled by a VTR of the VHS standard.
To provide compatibility with the VHS VTR, the S-VHS VTR is designed to record and reproduce a video signal in any one of the S-VHS format and the VHS format. During the VHS recording mode of operation of the VTR, the video signal is processed according to the VHS format. On the other hand, during the S-VHS recording mode of operation of the VTR, the video signal is processed according to the S-VHS format. If the S-VHS processing of the video signal includes a step of sub emphasis, it tends to be difficult to correctly separate a sync signal from the sub-emphasis-resultant video signal.
It is an object of this invention to provide a signal processing circuit for correctly separating a sync signal from a video signal.
It is another object of this invention to provide an improved signal processing apparatus.
A first aspect of this invention provides a signal processing circuit for use in a recording apparatus which operates in any one of a standard mode and a high-quality mode, the apparatus recording a video signal of a standard format during the standard mode of operation, the apparatus recording a video signal of a high-quality format during the high-quality mode of operation, wherein the video signal of the high-quality format is wider in frequency band than the video signal of the standard format. The circuit comprises first means for subjecting a first signal to a nonlinear emphasis process to convert the first signal into a second signal; second means for selecting one of the first signal and the second signal in response to whether the apparatus operates in the standard mode or the high-quality mode, and for outputting the selected signal as a third signal; third means for subjecting the third signal to a nonlinear de-emphasis process to convert the third signal into a fourth signal, the nonlinear de-emphasis process being inverse with respect to the nonlinear emphasis process; fourth means for selecting one of the third signal and the fourth signal in response to whether the apparatus operates in the standard mode or the high-quality mode, and for outputting the selected signal as a fifth signal; and fifth means for separating a sync signal from the fifth signal; wherein during the standard mode of operation of the apparatus, the first means selects the first signal, and the fourth means selects the third signal; and wherein during the high-quality mode of operation of the apparatus, the first means selects the second signal, and the fourth means selects the fourth signal.
A second aspect of this invention provides a signal processing circuit comprising first means for subjecting a first video signal to a nonlinear emphasis process to convert the first video signal into a second video signal; second means for selecting one of the first video signal and the second video signal, and for outputting the selected video signal as a third video signal; third means for subjecting the third video signal to a nonlinear de-emphasis process to convert the third video signal into a fourth video signal, the nonlinear de-emphasis process being inverse with respect to the nonlinear emphasis process; fourth means for selecting the third video signal when the second means selects the first video signal, for selecting the fourth video signal when the second means selects the second video signal, and for outputting the selected signal as a fifth video signal; and fifth means for separating a sync signal from the fifth video signal.
A third aspect of this invention provides a video signal processing apparatus comprising a first video signal processing circuit; and a second video signal processing circuit connectable to the first video signal processing circuit; wherein the first video signal processing circuit and the second video signal processing circuit comprise means for processing either a video signal of a standard format or a video signal of a high-quality format into a record signal in the presence of the second video signal processing circuit connected to the first video signal processing circuit, and the video signal of the high-quality format is higher in picture quality than the video signal of the standard format and is wider in frequency band than the video signal of the standard format; wherein the first video signal processing circuit comprises means for processing a video signal of the standard format into a record signal in the absence of the second video signal processing circuit; wherein the second video signal processing circuit comprises means for subjecting the video signal of the high-quality format to a nonlinear emphasis process to convert the video signal of the high-quality format into a first processing-resultant signal; and wherein the first video signal processing circuit comprises means for subjecting the first processing-resultant signal to a nonlinear de-emphasis process to convert the first processing-resultant signal into a second processing-resultant signal, and means for separating a sync signal from the second processing-resultant signal, the nonlinear de-emphasis process being inverse with respect to the nonlinear emphasis process.